Subtitle display by means of graphics has an important mission of conveying words uttered by the characters in a work, to people in every area of the world. One conventional technology for realizing subtitle display is the subtitle application of ETSI EN 300 743 standard (ETSI: European Telecommunication Standards Institute). The subtitle application is a video stream to be reproduced together with subtitle display by means of graphics. Here, the graphics that correspond to subtitle are displayed as a data stream of MPEG2 standard. The data stream is a sequence of PES packets, where each PES packet has a PTS (presentation time stamp). ETSI EN 300 743 standard defines the timing of subtitle display in a subtitle application. This standard establishes synchronization between a moving picture and graphics, in which graphics is displayed when corresponding images in a video stream are displayed.
When subtitle application is to be provided for BD-ROM, there is a need for further enhancing the resolution level of the graphics. To be more specific, the resolution level is desired to be improved to the level of 1920*1080. However, realization of such a high definition incurs an enormous amount of decoding load at reproduction.
The ETSI EN 300 743 standard defines reproduction control for performing decoding at the time designated by the PTS, and for displaying it straight away. When this is applied, an enormous amount of decoding load will be concentrated in the reproduction apparatus at points immediately before display. Such concentration of load forces the hardware/software competence of the reproduction apparatus to be high, so as to realize graphics display. If such a condition becomes essential for reproduction apparatuses, production cost for reproduction apparatuses will rise remarkably, which will prevent such reproduction apparatuses from being commonly used.